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Dwarf Stars

Most stars are classified as dwarfs, including the Sun. These stars lie on the main sequence, the phase of life in which a star steadily converts the hydrogen fuel in its core to helium. When the core hydrogen has been depleted, the star gets larger, cooler, and brighter. It becomes first a subgiant, then a giant. Especially massive stars may become bright giants or supergiants. Despite the "dwarf" moniker, many main-sequence stars are quite large, with some spanning several times the Sun's diameter. The Sun is classified as a G2V star; G2 indicates its surface temperature (around 10,000 degrees Fahrenheit/5,500 C), while the Roman numeral V designates its dwarf status.

Some classes of stars that are small have special dwarf classifications. Red dwarfs are only a fraction the size and mass of the Sun, and can be as little as one ten-thousandth the Sun's brightness. Because they are so cool, their surfaces are orange or red. White dwarfs are the dead cores of once-normal stars. They typically are less massive than the Sun, and only about the size of Earth. They are extremely hot and dense, although they no longer produce nuclear reactions.